This invention relates to machines in which one member is positioned relative to another. For example, it relates to coordinate measuring machines, machine tools, scanning machines and robots, in which a tool or probe is positioned relative to a workpiece.
More particularly, the invention relates to performing measurements or calibration on such machines.
In some aspects, the present invention is a development of the apparatus and methods described in our International Patent Application No. PCT/GB94/02593, published as WO95/14905, to which reference should be made. Reference is also directed to the apparatus and methods described in International Patent Applications Nos. WO91/03145 (Kearney & Trecker) and WO92/17313 (Geodetic Machines), and in European Patent Application No. 534585 (Ingersoll).
All the above applications show machines in which a tool, probe or other operator is mounted on one structure, for movement relative to another structure upon which a workpiece may be mounted. The tool, probe or other operator may be movable and the workpiece fixed, or vice versa. The relative movement is effected by six rams acting between the two structures. These rams can be controlled so as to produce any desired relative movement between the structure, with six degrees of freedom (three translational and three rotational). It is necessary to measure the movements of the rams, and one aspect of the present invention is concerned with such measurement.
A problem with the apparatus described in the various above-referenced patent applications is that of calibrating the movement of the machine. To achieve this, it is necessary to measure the relative position and orientation of the moving structure relative to the fixed structure, independently of the measurements of the extensions of the rams which produced that position and orientation. Another aspect of the present invention allows such calibration, both on the type of machine described in the above patent applications, and on more conventional machines.